--- a/ExtStream.st	Fri Mar 31 04:52:25 1995 +0200
+++ b/ExtStream.st	Sun Apr 02 13:07:58 1995 +0200
@@ -24,7 +24,7 @@
 COPYRIGHT (c) 1988 by Claus Gittinger
 	      All Rights Reserved
 
-$Header: /cvs/stx/stx/libbasic/Attic/ExtStream.st,v 1.32 1995-03-18 05:04:04 claus Exp $
+$Header: /cvs/stx/stx/libbasic/Attic/ExtStream.st,v 1.33 1995-04-02 11:06:23 claus Exp $
 '!
 
 !ExternalStream primitiveDefinitions!
@@ -87,7 +87,7 @@
 
 version
 "
-$Header: /cvs/stx/stx/libbasic/Attic/ExtStream.st,v 1.32 1995-03-18 05:04:04 claus Exp $
+$Header: /cvs/stx/stx/libbasic/Attic/ExtStream.st,v 1.33 1995-04-02 11:06:23 claus Exp $
 "
 !
 
@@ -163,10 +163,22 @@
       has big problems handling unbounded Streams, since the EOF handling in stdio is
       not prepared for data to arrive after EOF has been reached - time will show, if we need
       a complete rewrite for UnboundedStream ...
+
       Also, depending on the system, the stdio library behaves infriendly when signals
       occur while reading (for example, timer interrupts) - on real unixes (i.e. BSD) the signal
       is handled transparently - on SYS5.3 (i.e. non unixes :-) the read operation returns
       an error and errno is set to EINTR. Thats what the ugly code around all getc-calls is for.
+
+      Notice that typical stdio's use a single errno global variable to return an error code,
+      this was bad design in the stdio lib (right from the very beginning), since its much
+      harder to deal with this in the presence of lightweight processes, where errno gets
+      overwritten by an I/O operation done in another thread. (stdio should have been written
+      to return errno as a negative number ...).
+      To deal with this, the scheduler treats errno like a per-thread private variable,
+      and saves/restores the errno setting when switching to another thread.
+      (Notice that some thread packages do this also, but ST/X's thread implementation
+      does not depend on those, but instead uses a portable private package).
+
       Finally, if an stdio-stream is open for both reading and writing, we have to call
       fseek whenever we are about to read after write and vice versa.
       Two macros (__READING__ and __WRITING__) have been defined to be used before every
@@ -2390,7 +2402,7 @@
 	__immediateInterrupt__ = 1;
 	do {
 	    c = getc(f);
-	} while ((c < 0) && (errno == EINTR));
+	} while ((c < 0) && (errno == EINTR) && (clearerr(f), 1));
 	__immediateInterrupt__ = 0;
 
 	if (c != EOF) {